Winglets are there to counter the main vortex.
Like everything else they have some disadvantages too.
Probably what the designers try to do is balancing the counter of the main vortex to the creation of their own vortex...
If you put the winglets orizontally they will do the same job as the vertical ones, but slightly less efficiently.
But the benefit is that being orizontal they contribute to lift also, so this design seems to privilege an increase in MTOW (increased performance), loosing something in cruise.
Anyway they've reinvented the wheel, check this Dornier design which has been around for more than 20 years...
http://www.!!!!!!!!!!!!!!/open.file/348779/M/